Asphalt-based roofing materials, such as roofing shingles, roll roofing and commercial roofing, are installed on the roofs of buildings to provide protection from the elements. Typically, the roofing material is constructed of a substrate such as a glass fiber mat or an organic felt, an asphalt coating on the substrate, and a surface layer of granules embedded in the asphalt coating.
The typical roofing material construction is suitable under most circumstances. However, sometimes a roofing material is subjected to forceful impacts, such as impacts from hailstones during storms, which may cause significant damage to the roofing material. For instance, the force of the impact may cause a puncture or tear in the roofing material. Accordingly, there is a need for a roofing material having improved impact resistance.
Several patents disclose asphalt roofing materials constructed with multiple substrates. For example, U.S. Pat. No. 5,326,797 to Zimmerman et al. discloses an asphalt-coated roofing shingle including a top mat of glass fibers and a bottom mat of polyester. The patent is related to a fire-resistant shingle, and there is no mention of improved impact resistance. Also, there is no suggestion of improved bonding between the polyester mat and the asphalt coating.
U.S. Pat. No. 5,571,596 to Johnson discloses an asphalt-coated roofing shingle including an upper layer of directional fiber such as Kevlar fabric, a middle layer of fibrous mat material such as glass fiber mat, and a lower layer of directional fiber such as E-glass fabric. The upper fiber layer is described as being important to shield the shingle from hail impact damage. The lower layer of E-glass fabric is not effective for improving impact resistance of the shingle.
U.S. Pat. No. 5,822,943 to Frankoski et al. discloses an asphalt-coated roofing shingle including a scrim and a mat. The scrim is bonded to the mat with adhesive; there is no suggestion of improved bonding between the scrim and the asphalt coating. A scrim is not very effective for improving impact resistance of a shingle.
A journal article, "Ballistic Impact Resistance of SMA and Spectra Hybrid Graphite Composites", Journal of Reinforced Plastics and Composites, Vol. 17, 2/1998, by Ellis et al., discloses placing energy absorbing fibers on the back surface of a graphite composite. The fibers were found to provide only a slight improvement in the impact strength of the composite. The journal article is not related to roofing materials.
Thus, the previous literature does not suggest the specific positioning and bonding of a web, and the selection of the right material for the web, to effectively dissipate the energy of impacts on the roofing material.
It is known to manufacture roofing materials with rubber-modified asphalt to provide some improvement in impact resistance. Unfortunately, roofing materials made with rubber-modified asphalt are more difficult to manufacture, handle, store and install, and are more expensive, than roofing materials made with conventional roofing asphalt. Also, the rubber-modified asphalt shingles are not very effective in resisting impacts. Accordingly, there is still a need for a roofing material having improved impact resistance.